I have FC3 installed at the moment on a lucky star KT100 motherboard,
with 512SD RAM and AMD Athlon 1.4GHz proccessor. I just got a good deal
on a brand new Soltek motherboard, 512 DDR RAM and AMD Athlon 2.4GHz
processor. My question is, how will fedora handle this hardware upgrade,
first of all will it boot? The HDD an all other other hardware will
remain as they are.

I just don't want to try it before I ask someone.. don't want to do a
new install if not nessecary.

I already did that trick once.. Replacing a motherboard ECS k7vta3 (via
kt333 chipset) with an asus a7n8x (nforce 2).
At that time , I think I was using FC2. All the necessary stuff was
reconfigured automatically by kudzu.. I only had to change the network
config to static IP.
Considering that you are using FC2 or above , then probably you'll have
no problem at all...